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Subject[53/55] fs: call security_d_instantiate in d_obtain_alias V2
2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Josef Bacik <josef@redhat.com>

commit 24ff6663ccfdaf088dfa7acae489cb11ed4f43c4 upstream.

While trying to track down some NFS problems with BTRFS, I kept noticing I was
getting -EACCESS for no apparent reason. Eric Paris and printk() helped me
figure out that it was SELinux that was giving me grief, with the following
denial

type=AVC msg=audit(1290013638.413:95): avc: denied { 0x800000 } for pid=1772
comm="nfsd" name="" dev=sda1 ino=256 scontext=system_u:system_r:kernel_t:s0
tcontext=system_u:object_r:unlabeled_t:s0 tclass=file
Turns out this is because in d_obtain_alias if we can't find an alias we create
one and do all the normal instantiation stuff, but we don't do the
security_d_instantiate.

Usually we are protected from getting a hashed dentry that hasn't yet run
security_d_instantiate() by the parent's i_mutex, but obviously this isn't an
option there, so in order to deal with the case that a second thread comes in
and finds our new dentry before we get to run security_d_instantiate(), we go
ahead and call it if we find a dentry already. Eric assures me that this is ok
as the code checks to see if the dentry has been initialized already so calling
security_d_instantiate() against the same dentry multiple times is ok. With
this patch I'm no longer getting errant -EACCESS values.

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/dcache.c | 3 +++
1 file changed, 3 insertions(+)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1201,9 +1201,12 @@ struct dentry *d_obtain_alias(struct ino
spin_unlock(&tmp->d_lock);

spin_unlock(&dcache_lock);
+ security_d_instantiate(tmp, inode);
return tmp;

out_iput:
+ if (res && !IS_ERR(res))
+ security_d_instantiate(res, inode);
iput(inode);
return res;
}



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